Enzymatic treatment of tea leaves either continuously or batchwise, for the production of instant teas offers many benefits for the resulting convenience beverage product. These include better acid stability, color, clarity, cold water solubility, flavor and higher yield. Continuous processing of tea leaf with enzymes is an economical method of providing the necessary operating conditions of time, temperature, enzyme concentration and water for the enzymes to be effective. The high throughput needed for commercial production is also accommodated by continuous processing with minimal complexity compared to batch operation.
The long contact times required for enzymes to be used effectively makes batch processing complex and requires a large capital investment in equipment to provide the residence time. Continuous, plug flow treatment reduces the amount and complexity of equipment needed to treat tea leaf with enzymes and allows for easy integration to downstream continuous extraction process equipment. Consistent, reproducible results is a further benefit of continuous treatment.
Black tea is usually prepared by subjecting freshly picked tea leaves to a series of processing conditions including the withering and rolling of freshly harvested leaves, followed by a fermentation step (enzymatic oxidation) during which much of the characteristic color, flavor and aroma of black tea are developed. The fermentation is halted after a suitable period of time by "firing" or drying the tea at temperatures ranging from about 65.degree. C. to about 100.degree. C. to inactivate the enzymes causing the fermentation. This completes the development of the flavor and color of the tea product. The extent of fermentation varies, in commercial practice, from black to various gradations between green and black. Partially fermented teas are known as "oolong" teas. Green teas are made by firing green tea before fermentation has taken place. Green, oolong, and black tea each provide a beverage having distinctive flavor and color characteristics.
When conventional teas are extracted with cold water for short periods of time (less than 15 minutes), the tea beverage produced has a low concentration of extractable tea solids, a very light color and almost no tea-like taste. Water at temperatures of about 100.degree. C. is customarily employed by the prior art to obtain a satisfactory beverage.
Various procedures are known in the art for making cold water soluble instant tea powders by solubilizing tea cream obtained from black tea extracts, e.g., Herz, U.S. Pat. No. 2,831,772; Perech, U.S. Pat. No. 2,863,775. While each of these processes are successful to varying degrees in producing a cold water soluble instant tea powder, each has disadvantages. Most fail to provide a tea powder which, on reconstitution, gives a beverage having a natural flavor and color.
Sanderson et al. U.S. Pat. Nos. 3,812,266 and 4,051,264 employ tannase with green tea.
Tsai. U.S. Pat. No. 4,639,375 treats tea with a combination of tannase and one or more cell wall lysis enzymes but only, prior to extraction.
There is a substantial body of literature on the role of enzymes in tea manufacture, which has been summarized in two review articles, Sanderson & Coggon, ACS Symposium Series, No. 47, pp. 12-26 (1977); and Roberts, J. Sci. Food Agric., 3, 193-8 (1952).
U.K. Patent 1,249,932, relates to a process for the solubilization of tea cream and to the preparation of water-soluble tea concentrates by the use of an appropriate enzyme, especially tannase.
U.K. Patent 1,380,135, describes the preparation of a cold water soluble instant tea powder containing solubilized tea cream. The process of the '135 specification involves either separating cold water-insoluble tea solids from the hot water extracted tea and treating them with tannase or treating the hot water extract of tea with tannase without separation.
U.K. Patent 1,413,351, relates to a process in which unfermented (green) tea is contacted with tannase and is subsequently converted to black tea.
U.K. Patent 1,546,508, relates to a method of treating fresh green tea leaf with tannase.
U.S. Pat. No. 5,445,836 relates to a process for producing tea extract with reduced haze under refrigeration using tannase and glucose oxidase to treat decreamed tea extract.
U.S. Pat. No. 3,959,497, relates to enzymatic solubilization of tea cream by treating tea extract or tea cream with enzymes.
In the prior art tea polishing is accomplished in part by centrifugation of the tea extract. It was not known that the percent of tea solids in the extract was critical in obtaining a reduced haze final product.
It is an object of this invention to provide an enzymatic extraction for the treatment of black tea leaf which produces a high quality natural product with good acid stability having haze values of a final black tea beverage of less tan 50 as measured by a Hunter Colorimeter.
It is another object of this invention to provide an improved continuous process for enzymatic extraction of black tea leaf which produces a product having better acid stability, greater cold water solubility, better color and better clarity than conventional black tea extracts.
Yet another object is to overcome or substantially eliminate the many problems of the art.
These and other objects of the invention will be evident from the following disclosure.